I think one of the Nintendo Power editors said it pretty well many years ago.
I'm paraphrasing here: A hardcore gamer is someone who puts a lot of passion into the games they play.
I'd say that is pretty true. If someone plays Candy Crush or Madden or COD or Minecraft for a few hours or so a week without much passion other than the simple entertainment it's probably just a time waster or minor hobby.
And as far as gaming skill goes, pretty much any above average skilled player is probably a hardcore gamer. But not every hardcore gamer is skilled.
Lifetime Sales Predictions
Switch: 161 million (was 73 million, then 96 million, then 113 million, then 125 million, then 144 million, then 151 million, then 156 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 40 million (was 60 million, then 67 million, then 57 million. then 48 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima